Safety of low-molecular-weight heparin during pregnancy: a retrospective controlled cohort study

To study the safety of low-molecular-weight heparin (LMWH) treatment during pregnancy for the mother and the foetus.

Retrospective controlled cohort study. Six hundred and forty-eight pregnancies exposed to LMWH were compared with 626 unexposed pregnancies. Principal characteristics, indications for LMWH use, and maternal and foetal complications were reported for each pregnancy. Data were obtained from patients' electronic hospital records and analysed using Statistical Package for the Social Sciences Version 17.0.

The incidence rates of various pregnancy complications did not differ between the groups (LMWH group vs control group): 1.56% vs 1.1% for thrombocytopenia, 8.7% vs 6.5% for preterm delivery, 0.7% vs 0.3% for stillbirth, 1.4% vs 1.0% for severe pre-eclampsia, 2.7% vs 2.2% for foetal growth restriction, and 10.7% vs 7.8% for antenatal bleeding. One serious antenatal maternal haemorrhage occurred in the LMWH group (0.15%), but this was unrelated to LMWH use. The caesarean section rate and the amount of bleeding during delivery were similar in the two groups (21% vs 19% and 500 vs 450 ml, respectively). The risk of major blood loss during labour (>1000 ml) was no higher in the LMWH group compared with the control group. The incidence of allergic skin reactions was 0.3% in the LMWH group. No heparin-induced thrombocytopenia or symptomatic osteoporotic fractures were observed. Recurrent venous thromboembolic events occurred in 2.5% of patients in the LMWH group.

This study indicates that the use of LMWH is safe during pregnancy.